The present invention relates to an acoustic microscope device using an acoustic surface wave.
FIG. 1 shows a construction of a known acoustic microscope device. A gate signal generated by a gate signal generator 1 is supplied to a transmitting circuit 2 to gate transmitting output signals. Several tens waves thus gated are supplied via a circulator 3 to a matching box 4 in which an impedance matching is effected. The transmitting signals are further supplied to a vibrating element 5 made of piezoelectric material to produce an acoustic wave. The acoustic wave transmitted by the element 5 is focused by an acoustic lens 6 via an acoustic wave propagating medium 7 such as water onto a specimen 8. The acoustic wave reflected by the specimen 8 is collected by the acoustic lens 6 and received by the vibrating element 5 to produce a reflection signal. The reflection signal produced by the vibrating element 5 is supplied through the matching box 4 and circulator 3 to a receiving gate circuit 9 to which is also supplied the gate signal from the gate signal generator 1. The receiving gate circuit 9 selects only the reflection signal and the selected reflection signal is amplified and detected by a receiving amplifier 10. The output signal from the amplifier 10 is further peak-detected by a video process circuit 11. A specimen 8 is placed on a specimen holder 13 which is driven two-dimensionally by a mechanical scanner 12. Therefore, it is possible to obtain a two-dimensional distribution signal of the peak values of the reflection signal supplied from the video process circuit 11. This signal is converted into a television signal by means of a scan converter 14 and the television signal thus converted is displayed on a television monitor 15. The gate signal generator 1 and video process circuit 11 are synchronously driven by a clock generator 16.
In the known acoustic microscope device mentioned above, in order to increase a resolution of the displayed image it is necessary to increase the frequency of the acoustic wave. However, if the frequency is increased, the acoustic wave is decayed in proportion to a square of the frequency. For instance, the acoustic longitudinal wave of 500 MHz is absorbed in water of 20.degree. C. by 50 dB/mm, the water being usually used as the propagating medium 7. Therefore, the resolution of the known acoustic microscope device is limited. Further, the resolution may be increased by increasing a curvature of the acoustic lens 6. However, the curvature of the lens 6 could not be made large enough due to the fact that the lens might be close to the specimen 8 to an inadmissible extent.
The known acoustic microscope device has another drawback that the scanner 12 for scanning the specimen 8 mechanically is liable to be large in size and complicated in construction.